Gas atomization device and gas atomization method

Abstract

The present invention addresses the problem of providing a gas atomization device and a gas atomization method whereby it is possible to continuously produce a metal powder with a small particle size over a relatively long period of time and in which the adhesion of unsolidified metal powder is unlike to occur even though suction pipes or the like are used to form flow paths. A gas atomization device 10 according to the present invention comprises a gas nozzle 12, a molten metal supply section 11, and a flow path WY. The gas nozzle has a plurality of injection ports Po. The gas nozzle injects gas from the injection ports toward a focal point FP. The molten metal supply section supplies molten metal from the upper side of the focal point in the vertical direction toward the focal point. The flow path extends downward from the lower end of the gas nozzle so as to surround the injection ports in a plan view. The vertical distance De from the gas injection ports to the focal point is longer than the vertical distance Db from the gas injection ports to the lower end of the flow path.

Description

Gas atomizing device and gas atomizing method

[0001] The present invention relates to a gas atomizing apparatus and a gas atomizing method.

[0002] In recent years, free-fall gas atomization has become widely known as a method for producing metal powders of titanium, zirconium, and other metals that have high melting points and exhibit high activity at high temperatures. The "free-fall gas atomization" referred to here refers to a method for producing metal powders by melting a metal by induction heating or the like to form a molten metal, and then spraying an inert gas or air at high speed into the molten metal (see, for example, Patent Document 1).

[0003] The particle size of metal powder produced by gas atomization depends greatly on the flow rate of the gas injected from the gas nozzle. A method utilizing the ejector effect has been proposed as a method for increasing the gas flow rate to produce powder with a small particle size (see, for example, Non-Patent Documents 1 and 2). In this method, a flow path is provided in the direction of the gas injection port using a suction tube or the like, and the pressure can be reduced by the ejector effect. Furthermore, the ejector effect can be enhanced by reducing the diameter of the flow path, ultimately resulting in the production of powder with a small particle size.

[0004] Japanese Patent Application Laid-Open No. 2002-241807

[0005] Toru Takeda and Kazumi Minagawa, "Decompressed Gas Atomization of Bronze," Abstracts of the Japan Society of Powder and Powder Metallurgy, 1990, pp. 28-29. Tadanori Kojima and Yoshihiro Matsuoka, "Study on Interference of Underexpanded Jets," Transactions of the Japan Society of Mechanical Engineers, No. 88-0469B, 1989, pp. 188-193.

[0006] However, if the diameter of the flow path is made too small, unsolidified metal powder adheres to the inner wall of the suction pipe, etc., clogging the flow path, forcing the production of metal powder to be stopped, making continuous production of metal powder extremely difficult. In particular, when producing metal powder that exhibits high activity at high temperatures, such as titanium or titanium alloy, adhesion of unsolidified metal powder is likely to occur, making it extremely difficult to reduce the diameter of metal powder using a suction pipe, etc.

[0007] The object of the present invention is to provide a gas atomizing device and a gas atomizing method that are capable of continuously producing small particle size metal powder over a relatively long period of time while utilizing a suction tube or the like to form a flow path and while preventing adhesion of unsolidified metal powder.

[0008] A gas atomizing device according to a first aspect of the present invention includes a gas nozzle, a molten metal supply unit, and a flow path. The gas nozzle has multiple injection ports. The gas nozzle injects gas from the injection ports toward a focal point. The molten metal supply unit supplies molten metal from vertically above the focal point toward the focal point. The flow path extends downward from the lower end of the gas nozzle so as to surround the injection port in a plan view. The diameter of the flow path is preferably within a range of 40 mm to 160 mm, from the viewpoint of preventing adhesion of unsolidified metal powder to the wall surface of the flow path. The flow path may be formed by a tube, a block with a through hole, or the like. The vertical distance from the gas injection port to the focal point is longer than the vertical distance from the gas injection port to the lower end of the flow path.

[0009] As a result of extensive research by the inventors of the present application, it has been confirmed that the above-mentioned gas atomization device is less likely to cause adhesion of unsolidified metal powder, and is capable of continuously producing small particle size metal powder over a relatively long period of time.

[0010] In a gas atomization method according to a second aspect of the present invention, a gas atomization apparatus includes a gas nozzle having multiple nozzles and spraying gas from the nozzles toward a focal point, a molten metal supply unit supplying molten metal from vertically above the focal point toward the focal point, and a flow path extending downward from the lower end of the gas nozzle so as to surround the nozzle in a plan view. Gas atomization is performed by making the vertical distance from the gas nozzle to the focal point longer than the vertical distance from the gas nozzle to the lower end of the flow path. The diameter of the flow path is preferably within a range of 40 mm to 160 mm, in order to prevent adhesion of unsolidified metal powder to the wall surface of the flow path. The flow path may be formed by a tube, a block with a through hole, or the like.

[0011] As a result of intensive research by the present inventors, it has been confirmed that by using the above-mentioned gas atomization method, adhesion of unsolidified metal powder is less likely to occur, and small particle size metal powder can be produced continuously over a relatively long period of time.

[0012] 1 is a schematic diagram of a metal powder manufacturing apparatus according to an embodiment of the present invention, and FIG. 2 is a schematic diagram of a gas atomizing device constituting the metal powder manufacturing apparatus according to an embodiment of the present invention.

[0013] REFERENCE SIGNS LIST 10 Gas atomizing device 11 High frequency induction coil (molten metal supply unit) 12 Gas nozzle Db Vertical distance from gas nozzle to the bottom end of the flow path De Vertical distance from gas nozzle to focus FP Focal point Po Jet nozzle WY Flow path

[0014] Hereinafter, a metal powder manufacturing apparatus according to an embodiment of the present invention will be described in detail with reference to the drawings.

[0015] 1, a metal powder manufacturing apparatus 1 according to an embodiment of the present invention is mainly composed of a raw material supply unit 2, a gas atomizing device 10, a gas receiving container 3, and a recovery container 4. These components will be described in detail below.

[0016] (1) Raw Material Supply Unit The raw material supply unit 2 supplies rod-shaped metal raw material BM to the gas atomizing device 10. Note that the term "metal" as used herein may include not only pure metals but also alloys and the like.

[0017] (2) Gas Atomization Apparatus The gas atomization apparatus 10 is a free-fall type gas atomization apparatus that produces metal powder from rod-shaped metal raw material supplied from a raw material supply unit 2, and as shown in Figures 1 and 2, is mainly composed of a high-frequency induction coil 11, a gas nozzle 12, and a suction tube 13. These components will be described in detail below.

[0018] (2-1) High-frequency induction coil The high-frequency induction coil 11 heats and melts the rod-shaped metal raw material supplied from the raw material supply unit 2 to form a molten metal. The rod-shaped metal raw material is passed through the center of the high-frequency induction coil 11.

[0019] (2-2) Gas Nozzle The gas nozzle 12 is a substantially annular member and is disposed so as to surround the periphery of a lower extension of the axis of the high-frequency induction coil 11. As shown in FIGS. 1 and 2, the gas nozzle 12 is formed with a plurality of gas injection ports Po. As shown in FIGS. 1 and 2, the gas injection ports Po are arranged at equal intervals along a horizontal plane. Although only two gas injection ports Po are depicted in FIGS. 1 and 2, the number of gas injection ports Po may be three or more. Furthermore, as shown in FIG. 2, the focal points FP of the gas injection direction from these injection ports Po are located below the lower end of the suction pipe 13, i.e., inside the gas receiving vessel 3. In other words, in the gas atomizing device 10 according to this embodiment, the vertical distance De from the gas injection port Po to the focal point FP is designed to be longer than the vertical distance Db from the gas injection port Po to the lower end of the suction pipe 13, i.e., the lower end of the flow path WY. These gas nozzles 12 inject an inert gas (for example, a rare gas such as argon) onto the molten metal supplied from the high frequency induction coil 11 to powderize it.

[0020] (2-3) Suction Tube As shown in Figures 1 and 2, the suction tube 13 has a straight tube shape and extends downward from the lower end of the gas nozzle 12. The suction tube 13 is disposed so as to surround the injection port Po in a plan view. The axis of the suction tube 13 is aligned with the axis of the high-frequency induction coil 11. The inner diameter of the suction tube is preferably within a range of 40 mm to 160 mm, from the viewpoint of preventing adhesion of unsolidified metal powder to the inner surface of the suction tube.

[0021] (3) Gas Receiving Container The gas receiving container 3 serves to retain within the system the gas ejected from the gas nozzle 12 and the metal powder generated therein. As described above, the focal point FP of the ejection port Po is located inside the gas receiving container 3.

[0022] (4) Recovery Container The recovery container 4 serves to recover the metal powder produced by the gas atomization apparatus 10. A suction pipe is provided on the upper side of the recovery container 4, and this suction pipe is connected to a vacuum pump (not shown). That is, the gas ejected from the gas nozzle 12 is drawn by the pressure pump, and as a result, a gas flow is always formed toward the recovery container 4.

[0023] <Flow of Metal Powder Production by the Metal Powder Production Apparatus According to the Present Embodiment> Rod-shaped raw metal material BM is continuously supplied through the raw material supply unit 2 so that the tip of the rod-shaped raw metal material BM always faces the high-frequency induction coil 11 without contacting it. The high-frequency induction coil 11 sequentially melts the lower tip of the rod-shaped raw metal material BM, turning it into a molten metal, and the flowing molten metal is dropped into the gas receiving container 3 through the center of the gas nozzle 12. The molten metal is then powdered and scattered into the gas receiving container 3 as it passes through the inert gas flow AF ejected from the multiple ejection ports Po of the gas nozzle 12. The metal powder is then collected in the recovery container 4, which is connected to the bottom of the gas receiving container 3 by a pipe. The metal powder collected in the recovery container 4 is then sieved in the next step to be classified and separated into particle size ranges suitable for its intended use.

[0024] <Characteristics of the gas atomization device according to this embodiment> In the gas atomization device 10 according to this embodiment, the vertical distance De from the gas ejection port Po to the focal point FP is longer than the vertical distance Db from the gas ejection port Po to the lower end of the flow path WY. Therefore, when the molten metal is powderized, adhesion of unsolidified metal powder is less likely to occur, and small particle size metal powder can be continuously produced over a relatively long period of time.

[0025] <Modifications> (A) In the gas atomizing device 10 according to the previous embodiment, only one substantially annular gas nozzle 12 is provided, and multiple gas injection ports Po are formed in it, but multiple block-shaped gas nozzles each having one gas injection port Po may be arranged around the periphery of a lower extension line extending downward from the axis of the high-frequency induction coil 11.

[0026] (B) In the gas atomizing device 10 according to the previous embodiment, the flow path WY was formed by the suction pipe 13, but the flow path WY may also be formed by a block body or the like having a through hole formed therein.

[0027] (C) Although not specifically mentioned in the previous embodiment, the suction pipe 13 may not be a straight pipe but may have a shape that expands in diameter toward the bottom. Also, a pipe having an inner diameter larger than the inner diameter of the suction pipe 13 may be attached to the bottom end of the suction pipe 13, or a skirt portion that expands in diameter from the bottom end of the suction pipe 13 may be provided.

[0028] The present invention will be described in more detail below based on examples and comparative examples, but the present invention is not limited to these examples.

[0029] In the gas atomizing apparatus 10 shown in Figures 1 and 2, the vertical distance Db from the gas injection nozzle Po to the lower end of the suction tube 13 was set to 35 mm, the vertical distance De from the gas injection nozzle Po to the focal point FP was set to 46 mm, and the inner diameter of the suction tube 13 was set to 160 mm. Powdering of Ti-6Al-4V alloy was carried out using the metal powder production apparatus 1 shown in Figure 1. Argon gas was used as the gas used. As a result, Ti-6Al-4V alloy powder with an average particle size (D50) of 37.1 μm was successfully produced continuously over a relatively long period of time (see Table 1).

[0030] Except for changing the inner diameter of the suction tube 13 to 50 mm, powdering of Ti-6Al-4V alloy was carried out under the same conditions as in Example 1. As a result, Ti-6Al-4V alloy powder with an average particle size (D50) of 31.4 μm could be continuously produced over a relatively long period of time (see Table 1).

[0031] Except for changing the vertical distance Db from the gas injection port Po to the lower end of the suction pipe 13 to 20 mm, the Ti-6Al-4V alloy was pulverized under the same conditions as in Example 1. As a result, Ti-6Al-4V alloy powder with an average particle size (D50) of 38.3 μm was successfully produced continuously over a relatively long period of time (see Table 1).

[0032] Except for changing the vertical distance Db from the gas injection port Po to the lower end of the suction pipe 13 to 20 mm and changing the inner diameter of the suction pipe 13 to 50 mm, the Ti-6Al-4V alloy was pulverized under the same conditions as in Example 1. As a result, Ti-6Al-4V alloy powder with an average particle size (D50) of 33.0 μm could be continuously produced over a relatively long period of time (see Table 1).

[0033] Comparative Example 1 Powdering of Ti-6Al-4V alloy was carried out under the same conditions as in Example 1, except that the vertical distance Db from the gas injection port Po to the lower end of the suction pipe 13 was changed to 70 mm. As a result, the suction pipe 13 became clogged with unsolidified Ti-6Al-4V alloy powder in a relatively short time after the start of the process, making it impossible to continuously produce Ti-6Al-4V alloy powder (see Table 1).

[0034] Comparative Example 2 Powdering of Ti-6Al-4V alloy was carried out under the same conditions as in Example 1, except that the vertical distance Db from the gas injection port Po to the lower end of the suction pipe 13 was changed to 70 mm and the inner diameter of the suction pipe 13 was changed to 50 mm. As a result, the suction pipe 13 became clogged with unsolidified Ti-6Al-4V alloy powder in a relatively short time after the start of the experiment, making it impossible to continuously produce Ti-6Al-4V alloy powder (see Table 1).

[0035]

[0036] (Summary) In Examples 1 to 4, in which the vertical distance De from the gas injection nozzle Po to the focal point FP was longer than the vertical distance Db from the gas injection nozzle Po to the lower end of the suction pipe 13, small particle size Ti-6Al-4V alloy powder could be continuously produced over a relatively long period of time. However, in Comparative Examples 1 and 2, in which the vertical distance De from the gas injection nozzle Po to the focal point FP was shorter than the vertical distance Db from the gas injection nozzle Po to the lower end of the suction pipe 13, the suction pipe 13 became clogged with unsolidified Ti-6Al-4V alloy powder within a relatively short time after the start of the process, and continuous production of Ti-6Al-4V alloy powder was not possible.

Claims

1. A gas atomizing device comprising: a gas nozzle having a plurality of nozzles, which sprays gas from the nozzles toward a focal point; a molten metal supply section which supplies molten metal from vertically above the focal point toward the focal point; and a flow path extending downward from a lower end of the gas nozzle so as to surround the nozzle in a plan view, wherein the vertical distance from the gas nozzle to the focal point is longer than the vertical distance from the gas nozzle to the lower end of the flow path.

2. The gas atomizing device according to claim 1, wherein the diameter of the flow passage is within the range of 40 mm to 160 mm.

3. A gas atomization method in a gas atomization device having a gas nozzle with multiple nozzles that sprays gas from the nozzles toward a focal point, a molten metal supply section that supplies molten metal from vertically above the focal point toward the focal point, and a flow path extending downward from the lower end of the gas nozzle so as to surround the nozzle in a plan view, wherein gas atomization is performed by making the vertical distance from the gas nozzle to the focal point longer than the vertical distance from the gas nozzle to the lower end of the flow path.

Images